The damaging effects of radiation, particularly sunlight, on skin are well documented. Much damage is due to routine day-to-day activities in the sunlight.
The major short term hazard of prolonged exposure to sunlight is erythema (i.e., sunburn). The 290 to 320 nanometer wavelength ultraviolet radiation range, designated as the "UVB" wavelength range, tends to be the primary cause of erythema. The 320 to 400 nanometer wavelength ultraviolet radiation range, designated as the "UVA" wavelength range, also produces erythema.
In addition to the short term hazard of erythema, there are also long term hazards associated with UV radiation exposure. One of these long term hazards is malignant changes in the skin. Numerous epidemiologic studies demonstrate a strong relationship between sunlight exposure and human skin cancer. Another long term hazard of ultraviolet radiation is premature aging of the skin. This condition is characterized by wrinkling and yellowing of the skin, along with other physical changes such as cracking, telangiectasis (spider vessels), solar keratoses (growths), ecchymoses (subcutaneous hemorrhagic lesions), and loss of elasticity (sagging). The adverse effects associated with exposure to UVA and UVB wavelength radiation are more fully discussed in DeSimone, "Sunscreen and Suntan Products", Handbook of Nonprescription Drugs, 7th Ed, Chapter 26, American Pharmaceutical Association, Washington, D.C., 1982, pp. 499-511; Grove and Forbes, "A Method for Evaluating the Photoprotection Action of Sunscreen Agents Against UV-A Radiation", International Journal of Cosmetic Science, Vol. 4 (1982), pp. 15-24; and U.S. Pat. No. 4,387,089 issued to DePolo on Jun. 7, 1983. Although the immediate effects of ultraviolet radiation may be cosmetically and socially gratifying, the long-term hazards are cumulative and sometimes serious.
Sunblock agents are commercially available to protect the skin from UV radiation. These agents scatter or reflect ultraviolet radiation. Examples include titanium dioxide and zinc oxide. However, these agents are very susceptible to rub-off or wear-off, resulting in little or no protection.
The most common agents for sun protection are sunscreens. These agents exert their effects through absorption of ultraviolet radiation so that it cannot penetrate the skin. Sunscreens must remain on the surface of the skin during exposure to be effective. However, sunscreens are easily rubbed off or washed off by sweating or swimming and can also be lost by penetration into the skin.
In developing a new sunscreen, it is important that the material be safe and effective. In particular, it is not feasible to use a material which sensitizes the skin. Certain sunscreens are effective for a one time useage, however, on reapplication they may cause dermatitis. This phenomenon is known as sensitization and is usually noted as a reddening of the skin, a rash-like condition. Since sunscreens are used repeatedly it is important for a sunscreen not to be a sensitizer.
It is an object of the subject invention to provide topical pharmaceutical compositions which provide protection against damage to the skin from sun exposure and other radiation sources.
It is also an object of the subject invention to provide topical pharmaceutical compositions which provide protection against damage to the skin from sun exposure and other radiation sources while inducing little or no skin sensitization.
It is a further object of the subject invention to provide methods for preventing damage to the skin due to exposure of the skin to the sun and other radiation sources.
It is a still further object of the subject invention to provide methods for preventing damage to the skin due to metal-catalyzed free radical generation in the cells of the skin.
It is a still further object of the subject invention to provide methods of protecting the skin from radiation sources without marked sensitization of the skin.